Process of blow molding a food and beverage container with a melt phase polyester layer

ABSTRACT

A multilayered container and a process for forming the same are disclosed. The container includes a support wall formed from a plastic having an undesirable substance therein and polymerized to a level less than that necessary to prevent the undesirable substance from migrating from the plastic into the contents when the contents are in contact with the support wall. A protective wall is provided adjacent the support wall and adapted to be positioned between the support wall and the contents. The protective wall is formed from a material which limits the migration of undesirable substance from the support wall into the contents.

This is a continuation, of application Ser. No. 08/495,049, filed Jun.26, 1995, now abandoned.

BACKGROUND OF THE INVENTION

The present invention relates to plastic containers adapted to containfood and beverages whose taste and/or odor may be affected by thematerials of which the containers are made as well as by contaminantsgenerated in the course of their manufacture and use of the containers.In particular, the invention relates to containers produced frompolymers subject to degradation in the course of their conversion intocontainers, with the products of such degradation remaining entrappedwithin their walls and capable of diffusing into the contents, therebyaffecting the taste and odor thereof.

Similarly, the polymers may contain oligomers i.e., molecular fractionsthat have insufficiently polymerized, as well as unreacted monomers,both of which may diffuse into the contents of the containers, with thesame affect, as above. These conditions are encountered particularly inpolymers obtained by condensation reactions, such as polycarbonate,nylon, and also polyethylene terephthalate (PET), the polymerpredominantly used for beverage bottles and food jars.

To be suitable for use in food and beverage containers, PET must provideprotection of the contents against deterioration such as, in the case ofsoft drinks, loss of carbonation or chemical reactions due to exposureto ambient conditions. Further, depending on their intended use,containers may be subject to considerable internal pressure and forcesdue to handling and storage. Therefore, the grades of PET to be usedmust be able to impart physical properties for withstanding theseforces.

As is known, PET is a polymer that may be obtained in stepwisecondensation of terephthalic acid and ethylene glycol. Polymerization ismore complete the longer it is carried out at the appropriatetemperature, and it may be repeatedly interrupted. Up to a certain stageof condensation, the reaction is carried out in the "molten" phase i.e.,low-viscosity state, and is therefore termed a melt phase reaction, withthe product designated as melt-phase PET. As this phase of the reactionprogresses, the viscosity of the heated reacting mass increases to adegree, beyond which continuing manufacture is impractical. The polymerobtained at that stage, and even before, has many uses, notably for theproduction of textile fibers and film. However, melt-phase PET hasinsufficient physical properties and permeation resistance for use inlarge beverage bottles and certain other important packaging containers.Even more important, melt-phase PET entrains acetaldehyde (AA), anoxious product of thermal degradation, and also some oligomers, down toas yet unreacted monomer constituents, notably ethylene glycol. AA,which abbreviation stands for acetaldehyde, CH₃ CHO, is a liquid ofpungent-fruity odor that desorbs readily out of the walls of a containerthat is made from PET, in which the AA is entrained, into the contentsto spoil the odor and taste thereof, even in very small concentrations.Thus, typical specifications for soft-drink bottles call for an AA limitof 1 ppm, and even less for drinking water. Likewise, unreacted monomersand oligomers may enter the content of the container and may, apart frominterference with taste, constitute a health hazard as determined byprevailing laws regulating the same.

Accordingly, since AA is present in melt phase PET, the use of meltphase PET is not accepted for many forms of packaging, including some ofthe most important ones, i.e. beverage bottles. For the same reasonmelt-phase PET cannot be used even when its physical properties suffice,as in the case of small bottles that are subject to lesser stresses thanlarge ones, since these stresses rise in proportion with size.

In order to obtain PET without the drawbacks associated with melt-phasePET, polymerization/condensation has to be continued. Since it isimpractical to continue in the molten state, additional, expensiveprocesses are added, wherein the melt-phase product is cooled,comminuted to a particle size suitable to be suspended and heated in andby a stream of hot air. The product is heated in a solid-statepost-condensation reaction, preceded by crystallizing the melt-phasePET. Naturally, the cost of the finished PET increases substantially bythese steps.

The cost of polymerizing the feedstock into the bottle-grade PET nearlydoubles, compared with limiting the process to melt-phasepolymerization. Particularly when the physical properties of containersmade of melt-phase PET would otherwise suffice, as for small bottles,the increase in cost is accepted solely to eliminate excessive amountsof AA and other contaminants. In view of the fact that some 40% or moreof the total manufacturing cost of a PET bottle is represented by thecost of the PET, it is readily seen that the use of melt-phase resinwould represent great economic benefits.

There exists, therefore, a need for a container and process formanufacturing the container wherein melt-phase or scrap PET can be usedin the container having unrestricted application to food and beverage bynot contaminating the same.

SUMMARY OF THE INVENTION

The primary object of this invention is to provide a container andprocess which allows the use of PET that contains excessive amounts ofAA and other contaminants in beverage and food containers.

Another object of this invention is to provide a plastic container frompolymers that contain residues of their polymerization and/or othercontaminants in excess of the amount acceptable for use of the containerin packaging food and beverages.

It is a further object of the present invention to provide a simpler andmore economical process for manufacturing PET and other analogouspolymers for conversion into food and beverage containers for reducingmanufacturing costs.

In accordance with the present invention, the foregoing objects andadvantages may be readily obtained.

The container of the present invention includes a support wall formedfrom a thermoplastic having an undesirable substance therein capable ofmigrating from said support wall. Preferably, the support wall ispolymerized to a level less than that necessary to prevent theundesirable substance from migrating from the plastic into the contentswhen the contents are in contact with the support wall. In the preferredembodiment, the plastic is PET containing acetaldehyde in excess of 2ppm. A protective wall is provided adjacent the support wall and adaptedto be positioned between the support wall and the contents. Theprotective wall is formed from a material which limits the migration ofundesirable substance from the support wall into the contents, to atleast an acceptable level.

In one embodiment of the invention, the protective wall or barrierserves to avoid contamination due to acetaldehyde (AA) and substancesthat represent health hazards representing unintended, or unavoidableresidues as a result of the manufacturing processes from which the PETis derived.

In a preferred embodiment, the PET is polymerized in the melt-phase ormolten state only, without subsequent polymerization in the solid state,and the conversion thereof into containers is carried out in a mannerthat provides the physical properties necessary for their intendedservice, notably by sufficient bi-axial orientation.

A process for manufacturing the container of the present inventionincludes the steps of polymerizing a plastic containing an undesirablesubstance therein to a level less than that necessary to prevent theundesirable substance from migrating from the plastic into the contentswhen the contents are in contact with the plastic; combining the plasticwith a protective substrate and forming a composite, wherein theprotective substrate is formed from a material which limits themigration of the undesirable substance from the plastic into thecontents, at least to an acceptable level; forming the composite into anarticle comprising at least one of a precursor and a preform; and blowmolding the article into the container, wherein the protective substrateis positioned for contact with the contents. The precursor may be formedinto a preform.

In the process, the step of combining may comprise the step of extrudingthe plastic onto the substrate for forming the composite. Alternatively,the step of combining may comprise the step of co-extruding the plasticwith the substrate and forming the composite in one of the shape of asheet and tube, or co-injecting the plastic with the substrate.

In a particular embodiment, the protective substrate is a laminate whichmay include an outer adhesive layer and which includes an intermediatelayer of EVOH and an inner layer of PET having a low acetaldehydecontent, wherein said inner layer is adapted to be formed to bepositioned so as to contact the contents and shield the intermediatelayer of EVOH from the contents.

In place of EVOH, other substances may be used for the same purpose,e.g. acrylonitrile polymers and nylons, depending on the types ofcontaminants to be excluded and the abundance thereof in the containerwalls. In practice, the composition of the barrier layer or laminate iscalculated based on the laws of diffusion and the permeation propertiesand solubilities reported in the literature.

The above sheet or tube laminates may be economically produced in theplant which houses the melt-phase polymerization, preferably followed byproducing preforms therefrom by conventional pressure forming and/orcutting operations, the same operations conventionally performed torender plastic convenient to distribute, in the shape of pellets.

The details of the present invention are set out in the followingdescription and drawings wherein like reference characters depict likeelements.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will be more readily understandable from aconsideration of the following drawings, wherein:

FIG. 1 is a cross-sectional view of a container of the presentinvention;

FIG. 2 is an enlarged, partial cross-sectional view taken along lines2--2 of FIG. 1;

FIG. 3 is a cross-sectional view of a preform from which the containerof FIG. 1 is molded;

FIG. 4 is a schematic flow chart of the steps for manufacturing thematerial from which the container of FIG. 1 is to be made;

FIG. 5 is a schematic flow chart of alternate steps for manufacturingthe material;

FIG. 6 is a schematic representation of the manufacturing of a preformin accordance with FIG. 3, being made from the material manufacturedaccording to the process of FIG. 4; and

FIG. 7 is a schematic representation of the manufacturing of a preformin accordance with FIG. 3, being made from the material manufacturedaccording to the process of FIG. 5.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring now to the drawings in detail, there is shown in FIG. 1 aplastic container 10 for beverages or foods having an outer support wall12 forming a structural layer designed to withstand the mechanicalstresses imposed upon the container in the course of handling and use.Outer wall 12 is preferably made of PET, the mass of which entrainsreaction products such as oligomers, unreacted monomers, and/or othercompounds, for example, acetaldehyde (AA), and ethylene glycol. Thereaction products are present in sufficient quantity to reduce theaverage molecular weight of the mass substantially below that requiredfor performance of the container.

In polymerizing, the material of which outer wall 12 consists, such asin a production condensation reaction, the aforementioned reactionproducts remain absorbed in the mass upon cooling from the reactiontemperature. Upon renewed heating, which may be necessary for producingwall 12, as by molding into preforms for containers, the several abovementioned reaction products thereof as well as other undesirablesubstances can become mobile due to reduced viscosity and gas formation,and therefore, are able to move through the wall or other mass inaccordance with the solubility and pressure gradients that develop dueto heating. A similar problem exists when employing scrap with breakdownproducts therein which represent undesirable substances capable ofmigrating from the support wall. Accordingly, the aforementionedsubstances can tend to migrate out of wall 12 or other mass by diffusionor desorption and into contents enclosed by wall 12 when wall 12 is inimmediate contact therewith. Due to contamination effects, this resultis undesirable. These phenomena are extensively reported in publishedliterature.

An important example of this phenomena in the design of containers isseen by the production of polyethylene terephthalate, hereinafter PET,which is extensively used for beverage and food packaging and is thepreferred plastic for use in forming container 10. PET used forcarbonated beverage containers should have an average molecular weightcorresponding to an intrinsic viscosity (IV) in the range of 0.7-1.2,depending on the intended services, such as, for example, for use indirect contact with food and beverages. Polymerized to the degreenecessary to obtain this viscosity, PET contains less of the abovementioned undesirable substances than would interfere with its use informing beverage or food containers or bottles and accordingly a wallsimilar to wall 12 but subject to this process would substantially notexhibit the migratory reaction products discussed above. This is one ofthe main reasons for extending the condensation reaction in spite of thesubstantial incremental cost. Another reason is to obtain the mechanicalproperties required of certain containers.

However, a great number of containers do not require the mechanicalproperties of further polymerized PET. For example, carbonated beveragebottles of small diameter, such as 10-20 oz. bottles, do not require thesame strength material as larger containers. Accordingly, PET having anIV equal to 0.70 and below could be used, were it not for the effect ofundesirable substances or reaction products such as AA on taste, thatdesorb from the PET container wall into the beverage or food or otherunreacted monomers and unlinked monomers or oligomers which may diffuseinto food from the container in amounts not permitted by healthregulations.

In many instances, unlike the process disclosed herein for theproduction of container 10, an expensive process of polymerization isused for the purpose of avoiding the above undesirable substances.

According to FIGS. 1 and 2, use of PET polymerized to a lesser degree,as having an IV ranging between 0.55 and 0.65, is made possible bylining the container 10 or wall 12 with an inner protective wall 14 thatis able to minimize, or altogether eliminate, the entry of taste andodor-affecting substances such as AA into the contents of the container.

Inner wall 14 preferably contains or is a material that is impervious toundesirable substances, as AA and/or other unreacted monomers and/oroligomers discussed above by way of example. A particularly effectiveand preferable barrier material is EVOH which is substantiallyimpervious to AA, although it loses its efficacy when in contact withwater. Similarly, other suitable inner-wall materials fail to retaintheir desired properties when exposed to the characteristics of thecontents of the container. Further, some of these materials may not beused in contact with the contents, since they may also undergo changesin contact therewith. Also, some of the materials available andfunctional for the intended purposes of being impervious to AA do notreadily adhere to the outer wall 12, which can result in unsightly andnon-functional containers. An additional layer is therefore preferablyused.

Accordingly, and as shown in FIG. 2, inner wall 14 is preferably made ofa laminate 15 composed of several layers, each having a function. Forexample, in the case of an outer wall made of PET, there may be atie-layer of an adhesive 16 adjoining outer wall 12, preferably followedby a barrier layer of EVOH 18, and then by one of a layer of apolyolefin as polypropylene (PP) and a preferably thin layer of solidstate PET 20 having a low acetaldehyde content, as the means to protectthe EVOH layer from water contained in the beverage or food, all shownin exaggerated thickness for simplicity. Additional examples of barrierlayer material are Selar Nylon (DuPont), MDX6 Nylon (MitsubishiChemicals), acrylonitrate polymers, polyethylene naphthalate (PEN), andpolyolefin containing materials. The manufacture of such laminatedstructures, as by co-extrusion, is well known and widely practiced.

Accordingly, a process for manufacturing container 10 includes blowmolding a preform 22, shown in FIG. 3, whereby preform 22 exhibits aninner layer or wall 24 and an outer layer 26, corresponding to the outerand inner walls 12 and 14, respectively, of container 10 of FIG. 1.Inner wall 24 is preferably a laminate 27 having layers 28, 30 and 32corresponding to laminate 15 and layers 16, 18 and 20 discussed above.It follows that preform 22 is the primary article to be made from PETthat contains the contaminants referred to.

Several processes for the production of lined preforms are known,including one according to U.S. Pat. No. 4,149,645, and they are usablefor the purposes of this invention. However, they are unsuited to takefull advantage of the cost savings available, based on the process ofthe present invention, using a grade of PET that is preferablypolymerized to a lesser degree and with a higher AA content than thegrades normally used which are subjected to additional polymerizationhave low AA.

FIG. 4 illustrates schematically the process of producing at least aprecursor 33 of preform 22. Accordingly, and referring also to FIGS.1-3, PET is preferably polymerized to within the IV range of 0.55 to0.65 in station S1 and transferred to an extruder in station S2. Thetransfer from station S1 to station S2 may be effected without allowingthe PET to cool below the extrusion temperature, or enter the cooled andcomminuted state. Preferably, the PET is extruded uncrystallized as asheet 34, adapted to form wall 12, onto a substrate 36, as shown in FIG.6, adapted to form laminates 15 and 27. Referring to FIGS. 4 and 6,substrate 36 is preferably produced by co-extrusion in station S3 andjoined to PET sheet or wall 12 from station S2, a composite is then madethereby and entered into a pressure forming unit in station S3, equippedto produce preforms 22, or precursors thereof. The last named operationat station S3 is known and practiced, usually under the designation of"coupled thermoforming". The result of that operation is shown in FIG.6, in which several precursors 33 have been molded from the substrate orlaminate 36 and PET sheet 34, which are shown prior to being separatedfrom the sheet by trimming. After trimming, a skeleton scrap remainswhich may be recycled with or without separating its layers.

The reference to precursor 33 of preform 22 is made because the aboveprocess of thermoforming does not always conveniently produce all thenecessary features of the finished preform. For example, the necks ofmany preforms must be threaded, which would render thermoformingimpractical. In such case, the precursor is preferably made bythermoforming, meaning an article of equal weight and close dimensionsto preform 22 is made, designed so as to subsequently fit into a mold toprovide the final features such as, for example, dimensions and threads.These features may be achieved by a corrective operation such as, forexample, compression molding, in accordance with well known practices.

The precursors may be separated from sheet 36 in such a manner thatthere is substantially no scrap produced, as by trim cuts along lines 35as to provide a square top in a precursor instead of a round top.

An alternate method for forming the preform 22 and container 10 is shownschematically in FIG. 5. The PET product of polymerization, i.e. sheet34 obtained in station S1 and laminate or substrate 36, similar to asshown in FIG. 6, is transferred into an extruder at station S5 equippedto produce co-extruded tubes 40, as shown in FIG. 7. The practice ofco-extrusion is well known, and in the present case, the tube consistsof an outer layer comprising sheet 34 of the melt-phase PET or otherpolymer, corresponding to outer wall 12 of container 10 or outer layer26 of preform 22, and an inner layer comprising laminate or substrate36, as described above and corresponding to laminate 15 of inner wall 14of container 10 or laminate 27 of preform 22, emerging as tube 40 fromstation S5 and directed into station S6. In station S6, tube 40 ispreferably subdivided into tube segments, as indicated by the dottedlines of FIG. 7, forming precursors made up of the tube segments.

As a further alternative method (not illustrated) for introducing abarrier resin within the body of or adjacent to the PET layer or wall12, wherein the barrier resin is preferably similar to those used withreference to the discussion of the embodiments of FIGS. 4 and 5, aco-injected preform can be formed according to known practice or inaccordance with the process discussed in the above cited U.S. Pat. No.4,149,645. The barrier resin can be co-injected in a mold along with thestructural PET layer, having the undesirable substances, so that thebarrier resin forms the innermost layer of the preform and inhibits therelease of the aforementioned undesirable substances into the contentsof the container.

For all of the embodiments described above, it may happen that thematerial best suited to serve as a barrier, such as to the loss ofcarbonation, is also a suitable barrier to exclude AA, or vice versa, asin the preferred embodiment with EVOH, and also with PEN and nylons. Insuch cases, and as with container 10, the substrate in the form oflaminate 15 comprising inner wall 14 performs the double service ofretaining one substance within the container while excluding anotherundesirable substance.

It is to be understood that the invention is not limited to theillustrations described and shown herein, which are deemed to be merelyillustrative of the best modes of carrying out the invention, and whichare susceptible of modification of form, size, arrangement of parts anddetails of operation. The invention rather is intended to encompass allsuch modifications which are within its spirit and scope as defined bythe claims.

What is claimed is:
 1. A process for forming a container for holdingcontents, comprising the steps of:polymerizing in the molten phase, butnot the solid phase to form a melt phase polymerized thermoplasticpolyester, said polyester thereby retaining therein undesirablesubstances intrinsic to the polymerization reaction, wherein saidsubstances are products of the polymerization reaction includingunreacted monomers, oligomers and acetaldehyde, said acetaldehyde beingpresent in excess of 2 ppm, whereby the polymerization is carried out toa polymerization level leaving residual amounts of said undesirablesubstances therein in an amount capable of migrating from said polyesterinto said contents when said contents are in contact with saidpolyester; combining said melt phase polymerized polyester containingsaid residual undesirable substances with a protective substrate andforming a composite having a layer comprising said polyester and a layercomprising said protective substrate, wherein said protective substrateis formed from a material which limits the migration of said undesirablesubstances form said polyester into said contents; forming a preformhaving said layer comprising said melt phase polymerized polyester andsaid layer comprising said protective substrate; and blow molding saidpreform into said container, wherein said protective substrate ispositioned for contact with said contents.
 2. The process of claim 1,wherein said composite is formed into a precursor which is formed into apreform.
 3. The process according to claim 1, wherein said step ofcombining comprises one of (1) extruding said polyester onto saidsubstrate for forming said composite, and (2) co-extruding saidpolyester with said substrate to form said composite in one of the shapeof a sheet and tube, and (3) co-injecting said polyester with saidsubstrate.
 4. The process according to claim 2, further comprising thestep of compression molding said precursor to form features of saidpreform.
 5. The process according to claim 4, wherein said featuresinclude at least one of threads and predetermined dimensions.
 6. Theprocess according to claim 3, wherein between said steps of polymerizingand extruding said process further includes the step of maintaining saidpolyester at a temperature sufficient for said step of extruding.
 7. Theprocess according to claim 1, wherein said protective substrate is alaminate, said process further comprising the step of co extruding saidlaminate.
 8. The process according to claim 7, wherein said laminateincludes a layer of EVOH, and an inner layer comprising one of PEThaving a low acetaldehyde content and a polyolefin, wherein said innerlayer is adapted to be positioned so as to contact said contents andshield said intermediate layer of EVOH from said contents.
 9. Theprocess according to claim 7, wherein said laminate is a barrier toacetaldehyde.
 10. The process according to claim 1, wherein saidprotective substrate includes a barrier substance selected from thegroup consisting of EVOH, PEN, and nylon.
 11. The process according toclaim 1, wherein said step of forming is achieved via thermoforming. 12.The process according to claim 3, wherein during the steps of extrudingand forming, multiple preforms are formed, wherein each of said multiplepreforms emerge from a shared remaining portion of said composite,further comprising the step of trimming each of said multiple preformsfrom said remaining portion of composite.
 13. The process according toclaim 12, wherein as a result of said step of trimming said remainingportion forms scrap, further comprising the step of recycling saidscrap.
 14. The process of claim 12, wherein the step of trimmingproduces substantially no scrap.
 15. The process according to claim 14,wherein said multiple preforms have a square top.
 16. The processaccording to claim 1, wherein said polymerized polyester is PET havingan intrinsic viscosity of less than 0.70.
 17. The process according toclaim 16, wherein said intrinsic viscosity ranges from 0.55 to 0.65. 18.The process according to claim 1, wherein said polyester is PET notsubjected to polymerization in the solid state.
 19. The processaccording to claim 1, wherein said undesirable substance includesethylene glycol.
 20. The process according to claim 1, wherein saidundesirable substances include a monomer from which said polyester ispolymerized and an oligomer produced during polymerization of saidpolyester.